Insulating glass units and their manufacture are described for example in U.S. Pat. No. 5,961,759, EP-B-805254 and EP-B-714964. The spacer can be a hollow section, generally containing a desiccant, held between the glass sheets by one or more sealant materials. Such a hollow section can be metal, for example an aluminium box spacer such as that described in U.S. Pat. No. 4,817,354, or plastic or a plastic/metal composite as described in U.S. Pat. No. 5,460,862 or EP-B-852280. The spacer can be a mastic layer containing a desiccant and formed around a reinforcement such as a corrugated metal reinforcement, as described for instance in U.S. Pat. No. 5,270,091. The spacer can alternatively be a foamed plastics material containing a desiccant, held between the glass sheets by a sealant, as described for example in U.S. Pat. No. 5,156,894 or U.S. Pat. No. 4,994,309, or the spacer can be a thermoplastic spacer containing a desiccant, which can be used as both spacer and sealant or may be used with an outer sealant layer at the edge of the glass sheets as described in EP-B-916801.
Insulating glass units are widely used in construction, transportation and in manufactured appliances, and are widely exported and traded, often via interim distributors. There is a need for insulating glass unit manufacturers to be able to trace their products, particularly on site for units used in construction or from manufactured articles containing the insulated glass unit, to ascertain whether a unit is genuinely of their manufacture or to identify the source of a defective unit. WO-A-00/36261 describes a glass unit having an electronic label containing in memory digital data concerning the glass (a ‘chip’) affixed on the inner wall of one of the glass plates.
When such a chip is used, it is important that the chip is concealed from visual detection, even when the IG unit has not yet been glazed into the window frame. The importance of concealing the chip and placing it at an inaccessible place is recognized by WO-A-00/36261, which discusses at length concealing the chip by placing it on the inside surface of one glass pane at a peripheral location which is not visible from the outside in operating position. It further teaches placement of the smart chip in such a manner that it is rendered invisible when the glazing is placed in the rabbet. In terms of placing the RFID device at an inaccessible location, the Catrame patent teaches two options: the chip is either inside the glass unit near the periphery or, in the case of a glass unit comprising a laminated glass pane, embedded into the thermoplastic interlayer of the laminated glass pane. In either location, the chip can be easily visually detected prior to the unit being glazed into the rabbet of the window frame. Furthermore, both options are viable only in conventional glazing, where the glass unit is installed into a frame. A significant market exists for insulating glass units where the edge seal is freely exposed in curtain wall constructions such as in structural glazing or in point-supported glazing.
EP-A-1698455 published on 6 Sep. 2006 describes an electronic tag disposed between the sheets of a laminated glass panel. A shielding layer which interrupts the transmission of light is formed on one of the glass sheets. The electronic tag is coloured so that it is difficult to distinguish from the colour of the shielding layer when seen through the other glass sheet.